Roger, I could be totally wrong on this as I do not have any crawfish, but this is what I have been told. The crawfish will eventually migrate to all parts of your system eventually, because the eggs, babies, whatever you want to call them are so small they easily go through your screens and get to the other areas. Make your screens to small and now you cannot keep the flow going for them stopping up all the time. I do not think crawfish would be a huge money maker in a commercial system although there does seem the possibility for some benefit to having them, so if they brought in any revenue, well that would just be extra. If I was planning a home system or hobby system, i would definitely experiment with them. I do not think it would be economically profitable to try and build a DWR trough just for crawfish. To be hones I think they would do better with the plants in there. But that is just my opinion.